Models will be sought among non-mammalian taxa and mammals other than standard laboratory species which show some evidence of cognitive Event Related Potentials (ERPs). Selected species of fish, amphibians, reptiles, birds, and certain mammals (e.g. dolphins, bats, opossums) will be tested with semimicroelectrodes chronically placed on or in the brain. Main issues are: (i) The distribution of cognitive ERPs among classes and species: are they widespread or peculiar to higher taxa (e.g. mammals or amniotes or tetrapods) or to particular groups within a class (e.g. dolphins but not bats, parrots but not pigeons)? (ii) The characterization of responses: how are they altered by manipulating the situation, including probability of the target stimulus, and the attention or state of the subject. Parts of the brain will be explored in favorable species. Stimulus situations will include (i) artificial stimuli and natural, ethologically significant stimuli, (ii) missing stimuli in monotonous series, (iii) "oddball" stimuli of less than 10% incidence, arbitrarily different from the common stimuli in the series, (iv) oddball stimuli with ethological value, e.g. visual models of prey, vocal calls slightly different from others, (v) reinforced paradigms for CNV and discriminant P300-like waves, and (vi) in favorable species, tailored to their ethology, incongruous termination of a normal, expected sequence. Pilot experiments will be attempted, given suitable endogenous responses in favorable species, on graded levels of cognitive demand. If simple discrimination learning to criterion shows that ERPs can be used to score the learning, in lieu of overt behavior, we will try ERPs as a measure of retention, generalization, concept learning, tolerance of ambiguous cues, or reversal learning, to see whether ERPs can aid in evaluating cognitive grade among species. Pilot experiments will be attempted on the effects of drugs on favorable species. Within a three year project, much of this paragraph will probably be represented only by test experiments, to assess feasibility. Finding, validating and characterizing model species among lower vertebrates and non-standard mammals is regarded as a necessary antecedent to assessing the behavioral and cognitive significance of ERPs and to the future use of lower species for analytic physiology, anatomy and pharmacology of these waves.